The present application is generally related to the field of communications relating to an inground device and, more particularly, to advanced passive interference management in a directional drilling system, apparatus and associated methods.
A technique that is often referred to as horizontal directional drilling (HDD) can be used for purposes of installing a utility without the need to dig a trench. A typical utility installation involves the use of a drill rig having a drill string that supports a boring tool at a distal or inground end of the drill string. The drill rig forces the boring tool through the ground by applying a thrust force to the drill string. The boring tool is steered during the extension of the drill string to form a pilot bore. Upon completion of the pilot bore, the distal end of the drill string is attached to a pullback apparatus which is, in turn, attached to a leading end of the utility. The pullback apparatus and utility are then pulled through the pilot bore via retraction of the drill string to complete the installation. In some cases, the pullback apparatus can comprise a back reaming tool which serves to expand the diameter of the pilot bore ahead of the utility so that the installed utility can be of a greater diameter than the original diameter of the pilot bore.
Steering of a boring tool can be accomplished in a well-known manner by orienting an asymmetric face of the boring tool for deflection in a desired direction in the ground responsive to forward movement. In order to control this steering, it is desirable to monitor the orientation of the boring tool based on sensor readings obtained by sensors that form part of an electronics package that is supported by the boring tool. The sensor readings, for example, can be modulated onto a locating signal that is transmitted by the electronics package for reception above ground by a portable locator or other suitable above ground device. In some systems, the electronics package can couple a carrier signal modulated by the sensor readings onto the drill string to then transmit the signal to the drill rig by using the drill string as an electrical conductor. Irrespective of the manner of transmission of the sensor data and for a given amount of transmission power, there is a limited transmission range at which the sensor data can be recovered with sufficient accuracy. The transmission range can be further limited by active interference and passive interference. Active interference generally consists of sources of electromagnetic signals present in the operational region that can overwhelm the signal being transmitted by the system. Conversely, passive interference serves to block or distort the transmitted signal, which can lead to reduced range or, in some cases, inaccurate readings. One common source of passive interference is rebar. In addressing the deficiencies of the prior art, Applicants filed commonly owned U.S. patent application Ser. No. 14/845,231 (hereinafter the '231 Application), entitled COMMUNICATION PROTOCOL IN DIRECTIONAL DRILLING SYSTEM, APPARATUS AND METHOD UTILIZING MULTI-BIT DATA SYMBOL TRANSMISSION, which is hereby incorporated by reference in its entirety. The '231 Application is submitted to provide sweeping benefits over the then-existing state-of-the-art and continues to provide such improvements, however, the present Application brings to light still further advances and improvements particularly with respect to passive interference, as will be discussed in detail at appropriate points hereinafter.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.